A Method to Identify Convective Cells within Multicell Thunderstorms from Multiple Doppler Radar Data

Abstract

Convective cell identification methods, besides their operational utility, are useful to identify cells, to understand cell interactions within multicell thunderstorms, and to distinguish between convective and stratiform regions within mesoscale convective systems. The method developed in this note was utilized for research on cell interactions within the 9 August 1991 Convection and Precipitation/Electrification (CaPE) multicell thunderstorm. A critical component of such research is an objective method to accurately depict all significant convective cells within an evolving multicell thunderstorm. While conventional methods based upon radar reflectivity can be successfully used in identifying cells, especially when the cells are in their growth stage, the methods are not as useful during the later stages of cell growth. This is because updraft and precipitation cores are not collocated at these advanced stages, and thus the reflectivity (precipitation) core may not be a good indicator of convectively active regions. The method presented in this note uses four objective criteria to define and identify convective cells within multicell thunderstorms. These criteria are chosen from a prestorm proximity sounding using the air parcel theory. The four objective criteria and their threshold values for the CaPE storm included in parentheses are 1) a threshold updraft Wd (?8 m s?1), 2) a threshold cloud-layer depth Dd (?4.9 km), 3) a threshold updraft area Ad (?1 km2), and 4) cell origin within the planetary boundary layer indicated by the Wpbl (?3 m s?1) contour. Since the method is based upon upward motion and not reflectivity factor, multiple Doppler radar data are required to utilize this method.